Morphological characterization and genetic diversity analysis of Tunisian durum wheat (Triticum turgidum var. durum) accessions

Abstract

Background Tunisia is considered a secondary center of diversification of durum wheat and has a large number of abandoned old local landraces. An accurate investigation and characterization of the morphological and genetic features of these landraces would allow their rehabilitation and utilization in wheat breeding programs. Here, we investigated a diverse collection of 304 local accessions of durum wheat collected from five regions and three climate stages of central and southern Tunisia. Results Durum wheat accessions were morphologically characterized using 12 spike- and grain-related traits. A mean Shannon-Weaver index (H′) of 0.80 was obtained, indicating high level of polymorphism among accessions. Based on these traits, 11 local landraces including Mahmoudi, Azizi, Jneh Khotifa, Mekki, Biskri, Taganrog, Biada, Badri, Richi, Roussia and Souri were identified. Spike length (H′ = 0.98), spike shape (H′ = 0.86), grain size (H′ = 0.94), grain shape (H′ = 0.87) and grain color (H′ = 0.86) were the most polymorphic morphological traits. The genetic diversity of these accessions was assessed using 10 simple sequence repeat (SSR) markers, with a polymorphic information content (PIC) of 0.69. Levels of genetic diversity were generally high (I = 0.62; He = 0.35). In addition, population structure analysis revealed 11 genetic groups, which were significantly correlated with the morphological characterization. Analysis of molecular variance (AMOVA) showed high genetic variation within regions (81%) and within genetic groups (41%), reflecting a considerable amount of admixture between landraces. The moderate (19%) and high (59%) levels of genetic variation detected among regions and among genetic groups, respectively, highlighted the selection practices of farmers. Furthermore, Mahmoudi accessions showed significant variation in spike density between central Tunisia (compact spikes) and southern Tunisia (loose spikes with open glume), may indicate an adaptation to high temperature in the south. Conclusion Overall, this study demonstrates the genetic richness of local durum wheat germplasm for better in situ and ex situ conservation and for the subsequent use of these accessions in wheat breeding programs.

SNP-Based Genetic Structure of Tunisian Durum Wheat Landraces and Distribution of the Resistance to Septoria Tritici Blotch

“…Durum wheat population structure study also help deciphering new sources of resistance to cope with challenging abiotic and biotic stresses, notably STB, one of the most devastating fungal disease on durum wheat crop. In the present study, we genotyped 366 Tunisian durum wheat accessions belonging to 13 old Tunisian landraces [22], collected from three central and two southern regions in Tunisia, using 286 SNPs derived from a High-density 90K wheat SNP array [60]. This study revealed the population structure and the genetic distribution of the resistance to Z. tritici in the Tunisian durum wheat landraces.…”

“…Recently, Ben Krima et al [30] showed a complex structure of 14 Tunisian durum wheat populations that was not entirely related to their geographic origin and variety name. However, Ouaja et al [22] identi ed a strong correlation between the genetic structure of 11 Tunisian durum wheat landraces and their morphological characterisation and nomenclature. Therefore, various interacting factors were reported that have in uenced the structure and evolutionary dynamics of durum wheat in Tunisia and the Maghreb region overall, among which complex selection trajectory, the signi cance of variety names, the occurrence of heterogeneous mixtures within populations, local adaptation, local and regional exchanges between farmers and, loss and misidenti cation [22,30,31].…”

“…However, Ouaja et al [22] identi ed a strong correlation between the genetic structure of 11 Tunisian durum wheat landraces and their morphological characterisation and nomenclature. Therefore, various interacting factors were reported that have in uenced the structure and evolutionary dynamics of durum wheat in Tunisia and the Maghreb region overall, among which complex selection trajectory, the signi cance of variety names, the occurrence of heterogeneous mixtures within populations, local adaptation, local and regional exchanges between farmers and, loss and misidenti cation [22,30,31]. After the Green revolution, old durum wheat landraces were mainly grown and managed by smallholder farmers under low-input traditional agrosystems in the marginal areas of Mediterranean region, notably in southern Europe and North Africa [4,32] as they were progressively abandoned from the early 1970s and replaced by improved genetically uniform modern varieties/cultivars [33,34].…”

“…In Tunisia, durum wheat landraces are still cultivated by low-input farmers, in northern and central mountainous areas, under traditional farming systems. These landraces, transmitted by farmers from one generation to the next, are designated by a variety name linked to a historical origin, regional location and speci c phenotypic characteristics [22,30].…”

Diversity of Cowpea [Vigna unguiculata (L.) Walp] Landraces in Mozambique: New Opportunities for Crop Improvement and Future Breeding Programs

“…Morphological traits have for years formed the backbone of breeders' attempts to capture the phenotypic differences among genotypes not only in cowpea [22], but also in several other crops worldwide [23][24][25]. These traits are a straightforward tool to estimate diversity and select parental lines for crossing [23], particularly in financially constrained agricultural research and development contexts such as the ones occurring in Africa.…”